I tried this approach with my current Swift project, but I found that it doesn't scale to a certain level of complexity. A ton of the UIKit APIs are naturally s

I tried this approach with my current Swift project, but I found that it doesn't scale to a certain level of complexity. A ton of the UIKit APIs are naturally stateful, so you end up having to work around them in weird ways. Animation is particularly hard when your view controllers are pure. The solution I opted for was to instead create a unidirectional data flow and just "refresh" the state of the VC every time it gets passed different data. This way, you get most of the benefits of one-way data flow and the state of your VCs is (somewhat) pure, but you can easily drop down and use the UIKit APIs as needed.